Champion R15B Compressor Pumping Air Slower Than Rated Capacity

by Terry
(East Texas)

I have recently mounted a used Champion R15B compressor to an 80 gallon tank. It has a 16.5 inch flywheel and is attached to a 5 HP 220 Volt motor spinning at 3450 RPM. The electric motor has a 3.5 inch pulley. According to my calculations, this is spinning the compressor pump at approximately 730 RPM. The pump is listed at 710 RPM max, so not sure if this small percentage of increase has anything to do with it, but the compressor pump seems to be only delivering about half of rated capacity, or less. From zero to shut off at 125 psi, it takes 14 minutes to fill. At lower pressures, say up to 50 psi, it appears to be pumping at about 8 to 9 CFM, but after that it drops off, and the best I can tell by the time it gets between 100 and 125 psi, its probably only pumping about 6 CFM or less. This pump is rated at 16.5 CFM at 175 psi.

I can find no visible or audible air leaks. I removed all four valves, and cleaned and inspected those. Unfortunately they were not gunked up, and appeared to be in good condition, with no carbon deposits, just some sticky oil residue, which I cleaned off with gasoline, and reassembled. This did not help, really.

What I have done to troubleshoot:

1. Changed oil in compressor. ( 30 weight non detergent motor oil )

2. Tried running the compressor without air filter to see if any change. None noticed

3. Ran compressor without intercooler tube attached to check each piston. Both were functioning independent of the other.

4. Checked for belt slippage

5. Removed the tubes from governor housing to see if air was blowing right through while running. Lots of air flow through tube coming from high pressure port to governor
housing, as expected. But, air flow seemed minimal from governor housing back to intake manifold. So unless air is dumping back into the crankcase, I believe the unloader valve is functioning as designed.

6. It has an oil monitoring device on it. I disconnected the tube from governor housing and plugged it in case that was a source of escaping air. No change.

7. Removed the valves again, and put a couple of tablespoons of Marvel Mystery Oil on top of each piston and allowed to soak for 30 minutes or so, then soaked out with a paper shop towel. After reassembly, no noticible change. The best I could tell, the pistons and cylinder walls looked really clean and shiny.

8. Checked for excessive blow by in crankcase. The best I can tell, its minimal.

So, I am at my wits end and exhausted my knowledge as to why this compressor is not pumping much air. I had a B5900 pump mounted on it previously, that could fill the tank from zero pressure in about 8 or 9 minutes all the way up to 175 psi Same electric motor, just different pulley. The B5900 pump developed a reed valve problem or head gasket problem was why I changed out to begin with.
I may have to fix it if I can't get this Champion to pump much better.

Any ideas what may be wrong with the Champion R15B ??

Bill says...

Terry, I am in awe of your expertise with compressors. You should be writing this column, not me!

If the compressor rings are good, and air is being compressed, all I can think of that you haven't already examined is an internal gasket leak.

Good luck, and thank you for the detail. If there are compressor mechanics out there that have a comment on Terry's work, please post.


Comments for Champion R15B Compressor Pumping Air Slower Than Rated Capacity

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Jul 11, 2017
Unloader leak
by: Anonymous

You mentioned air from intake line to unloader housing was minimal? I don't think you should have any air at all from intake when compressor is running.

You might try cleaning the ball and spring part of the governor valve. I guess if its minimal, it wouldn't cause whats happening. Sounds like its worn out a little. Just a guess.

Mar 01, 2015
by: Bruce

How did you identify you head as a R10D?

I've got a PL series and wonder if it was a R10 or R15.


Nov 09, 2014
by: Anonymous

you can take the unloader 1/4' line and plug it at the hp side and see if that makes a change.

on the back of the R15B there is a nut in the middle of the unloader make sure the spring and little white ball is clean of trash plus check the little pin that the ball and spring pushes on it that makes the unloader vent back in to the crank case.

now another question???

are the valve seats clean and the copper gaskets clean and no trash or carbon in the seats this will make one heck of an issue. Is the Heat Discharge tube clean of oil and carbon????

Jan 21, 2014
by: Anonymous

Check the unloader on the R15B and Fly weights for proper operation If the unloader is leaking by it blows back into the 1 stage by the air filter

Mar 16, 2011
by: P Smith

Thank you for all your help. The web site did show me what is needed for th R-15 pump. PAS

Bill says.... and my thanks to all of the posters that new what they were talking about and took the time to add their comments. That's what makes this site so useful. I'm happy to share what I do know, yet it's the many folks that have more info about a specific compressor and it's problems posting that really do the support. So, again, thanks to all of you.

Mar 15, 2011
Air Unloader
by: Terry

PAS, It sounds like ypou are describing the air unloader on some Champion R15B pumps. It serves two purposes,
1. to unload the air pressure from the high pressure line into the tank, and
2. to drain condensation from the line AND from the bottom of tank at the same time.

This vendor site displays a Champion compressor with this auto drain setup. Check the picture.

Mar 14, 2011
Model R-15 Pump
by: Paul Smith

I am putting together a 1974 Champion Model R-15 with 80 Gallon tank made by Kargard. I do not know what line is missing or going to from the compressor Housing at the back of the compressor. It is located on the bottom & looks like it may have went to an extension on the tank. The extension looks like water or air release valve. It has a place for a small tube before the shut wing nut. I would like to know what is it for & is this the correct hook up. Sincerely, PAS

Mar 10, 2011
Champion Pulley Size
by: Terry

Paul S., In response to your question on motor and pulley size, first I am wary of Sears HP ratings on compressor motors. This pump needs a true 5HP motor drawing 22-25 amps at rated capacity. If you have a Sears motor that draws 16 amps or so, it probably can't run this pump, at least not at top RPM. You can use a smaller pulley, and turn less pump RPM, and that motor should do fine. But, if you have a true 5 HP motor, and want full pumping capacity out of your Champion R15B pump, and if you have the original 16 1/2 inch Champion pump pulley, you want to use a 7 to 7 1/4 inch double motor pulley, which will yield a pump RPM of around 740 RPM. I am enclosing a Grainger web link that will give you all the info on that pump you need. Check it out.

As far as your other question, that is not enough information to help you. Sorry

Mar 09, 2011
Champion pumps
by: Paul Smith

I have two Champion compressors that I need information. 1-Model R-15. What motor size is needed for this pump? I have a 5 hp motor 1750 rpm from a Sears compressor to use. What Pulley size for the pump?

Also I have an older champion pump--2 clinders/ Serial pump # 60459 with an 18 inch pulley. What motor to use & the CFM did it put out.It is mounted on a stand as part of the unit.
All help gratefully appreciated.

Mar 08, 2011
Parts Locations for Champion Compressors
by: Terry

Grainger is where you are most likely guaranteed a part. I have been told that some auto parts stores carry Champion parts, but I do not know that first hand. I definitely know that Grainger carries parts, and can even send you a parts list upon request. Good luck.

Mar 06, 2011
need champion parts
by: c- nix

where can i get parts like this model ? I need the two bolt fitting that bolts to the compressor head and has the air cooled tubing going to it? please help.........

Aug 09, 2010
Follow up 8-9-10 Found it
by: Terry

Well, Duh, I found the problem. I was told it was a Champion R15b pump, and there is no markings or name plates on the compressor pump to label it. So I decided to check the stroke, and I removed the intake manifold and intake valve on the LP piston. And after carefully measuring stroke while rolling it over by hand, I discovered a revelation. It has a 2 inch stroke, which makes it a Champion R10D pump. The R15B pump has a 3 inch stroke. Cylinder bores are the same on each, and they look identical on the outside.

Bottom line, the R10D pump I have is probably pumping close to its normal capacity, according to some Champion pump data I have found.

Probably a little too late to take it back to the fellow who sold it to me, and let him know its not what he said. In reality, he may not have known himself.

Sorry if I led anyone down a wrong path.


No problem! It was a nice path.


Jul 26, 2010
Taking you up on your offer....
by: Terry


I decided to take you up and try a contribution on the B5900 2 stage compressor pump issues I have. I posted a separate comment for it and included some pics of the B5900 while it was tore down, plus some of my repair techniques, however amateur or professional they may seem. Beauty is in the eye of the beholder I guess. Anyway, perhaps it may help some of your readers on troubleshooting and repairing the top end of that particular pump.


Excellent, and thanks.


Jul 26, 2010
Follow up 7-26-10
by: Terry

Thanks, Bill, for your kind comment. I'm not a professional compressor mechanic, but in general I consider myself to be good at repairing things.

Just a follow up report. I decided to remove the High pressure port tube to the governor housing all together, because my existing pressure control valve had a built in unloader valve and drained off pressure when electric motor shut down. I can see no real need to have two sources to unload pressure on the piston. I plugged the port at the HP piston exhaust and at the governor housing. I left the tube connected running from the governor housing to the Low Pressure piston intake manifold, because that appears to be the only source of outlet for any crankcase blow by pressures, which as you know, could blow out my crank shaft end seal.

Pumping capacity by removing the HP port tube increased dramatically, but still not what it ought to be. I got out the calculator and from bore and stroke and pump RPM, this compressor on the big low pressure piston has a 21 cfm displacement capacity at zero pressure free air flow. Of course that would start dropping immediately with pressure build.

It now is pumping about 9 cfm between the 95 psi cut in pressure I have set up and the 125 psi cut out pressure. Time from cut in to cut out is 2 min 27 sec. It was originall taking 4 min 10 sec to pump same colume and pressure. I still believe this particular compressor is capable of pumping around 16 to 18 cfm at these pressures, so I am still thinking a strategy. My thoughts right now are that the piston rings are stuck or damaged. And possibly the valves are not as good as they could be.

So, when I can do without this compressor during break down / repair period, I will remove the cylinder and pistons and examine closely. I have a little 20 gallon Sears compressor that can fill in for awhile.

I'll keep you posted and possibly send some disassembly pics when I do.

Thanks for your forum,
You are most welcome, Terry. Thanks for your comments and your expertise. Feel free to chime in on any other issues here that you are comfortable offering advice on. With the number of inquiries I get, and some of them esoteric, I can use all the help I can get. :-)



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Champion Compressor - Will this motor hold up?

by Paul Smith
(Valdese, NC, USA)

I have a Westinghouse 5 hp motor-1750 Rpm Single phase-15 to 16 amps. Motor pulley is 4 inches. This was on an 80 gallon Sears/ compressor / tank from 1974. In your opinion, Will this motor hold up to a 1974 Champion R-15 pump if I use an 18 inch pump wheel instead of the 16.5 inch? I do understand this is about half the capacity of the original Champion motors that had a 7 inch pulley. Sincerely, PAS

Bill says....

Hey Paul. I haven't a clue.

Maybe some of this websites readers can comment?



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When it goes to start back up it trips the breaker?

by tom
(monrovia california)

1980 champion cv1 ser#330294

compressor runs great when it goes to start back up after using a tool it trips the breaker
Tom, empty the air from the tank. Start the compressor. Does it start OK?

If so, do it again. If it starts and runs to cut out with no problem the second time, then I would suspect the unloader valve as being the problem with your compressor not starting.

If the compressor will not start when it has no air in the tank, please comment here with that information.

If you are not sure about what the Unloader Valve does, please see that page on this site for information.



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Champion ci110 will not cut off

by Martin

Hi got a champion dominator ci110 dominator the issue is it will not cut off in automatic mode after it reaches pressure - tried shutting isolating valve off so no air leaking in air line system.there is a timer in the electric box could this be a fault thanks

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May 16, 2017
Champion R-15
by: Dennis

Have a
used Champion with ( Dennis, sorry, this comment is off topic. Please start a new post in this forum, then we can try to get you some answers about your compressor problem. Thanks. - Moderator )

Jul 16, 2012
Champion will not cut off
by: Buster

A lot of info missing here. Assuming this is a 3 phase control, could be several things wrong. You say it keeps running after reaching pressure, does the safety valve lift? Not sure how big it is, but some compressors run on load after the pressure set point is reached, they unload and the motor runs for a period in case the pressure drops and the demand goes up, it loads back up, without stopping the motor, that may be what the timer you reference to is for? If the motor continues to run after the pressure is reached, listen for a noise like a valve opening, the unloader, then watch the pressure gauge. It could also be an electrical component with welded contacts or stuck contactor!!
Let me know if this helps!


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